1. Field of the Invention
The present invention relates to cargo container lifting spreader compensating mechanisms, and more particularly, to a lifting spreader compensating mechanism for facilitating the engagement by the spreader with cargo containers having outof-plane twistlock engagement receptacles.
2. Description of the Prior Art
One of the problems for cargo container handling equipment which has been particularly difficult to accommodate is the engagement of damaged cargo containers by the standard equipment when the twistlock engagement receptacles formed in the top corners of the cargo containers have been moved out of alignment by deformation of the cargo container.
Another problem in cargo container handling results from designs for lifting spreaders which permit unequal loading of the twistlock mechanisms which shortens the life expectancy of the overloaded lug members.
A standard cargo container lifting spreader is designed to accommodate vertical twistlock misalignment of plus or minus one-quarter (.+-.1/4) inch. Therefore, if a cargo container has been damaged, usually by dropping or overloading, it is possible that the positioning of the twistlock engagement receptacles at the upper corners of the cargo container have been moved out of the plane of alignment in the upper surface of the cargo container by deformation thereof. If this occurs, the cargo container is thereby generally rendered unusable, but it is often the case that the condition occurs at a time when it is still necessary to engage the container in order to be able to move it to a destination where it can be unloaded and then taken out of service. In addition, some cargo containers are deformed out of alignment by simple overloading or in such a small manner that it is not easily noticeable or readily detectable, whereby the container remains in service and must be handled by the standard equipment. It is therefore necessary to make the equipment adaptable to be able to accommodate cargo containers which are slightly out of alignment as well as those that are substantially out of alignment in the extreme circumstance.
The prior art has not provided any means to accommodate deformed cargo containers which exceed the tolerance of plus or minus one-quarter (.+-.1/4) inch of misalignment of the twistlock receptacles disposed at the corners of the cargo container. In such a situation, the twistlock lug members will not engage the container or possibly not unlock if the damage occurs after the container has been lifted or engaged.
In an effort to reduce weight and increase adaptability for handling different lengths of containers, the design of cargo container lifting spreaders is tending toward a single telescoping beam with end cross-members which carry the twistlock male members. The simplest form of this design is a sliding beam which is comprised of two offset members disposed parallel to each other and which overlap in the middle portion of the beam. They are interconnected at the center of the beam with a reciprocating mechanism which actuates the two members causing them to slide back and forth with respect to each other whereby their combined length can be telescoped from one length to another. The inherent problem with the design is that the end cross-members are attached to the offset sliding members at positions which are not at the center of gravity of the end cross-members. This offset attachment results in a moment or torque in each member of the sliding member. However, the two sliding members experience opposite torques whereby they are offsetting and the system is balanced. Unfortunately, the design results in unequal loading of the twistlocks and excessive wear of the overloaded twistlock lug members disposed at the ends of the cross-members. In addition, it suggests to some purchasers of the spreader design that the twistlock lug members might hang out of plane under the spreader.
The present invention uniquely provides a solution to the diverse problems caused both by damaged cargo containers and by designs of lifting spreaders which permit unequal loading of the twistlocks, and it can be adapted to most types or designs of lifting spreaders.